Engine accessories may provide desired vehicle functions via consuming a portion of engine torque. The amount of torque consumed by an engine accessory may vary depending on the type of accessory and the level of output the accessory is providing. For example, one engine accessory may be an alternator. The alternator may supply electrical power to operate vehicle electrical systems and components such as vehicle lighting, electrical actuators, and sensors. The amount of engine torque consumed by the alternator to operate all vehicle electrical devices may vary as electrical devices are turned on and off. Consequently, engine speed can vary more than is desired by applying and releasing electrical loads from an alternator coupled to an engine. Additionally, other engine accessories may also consume engine torque without any knowledge of how much engine torque other engine accessories are consuming. As a result, the load applied to an engine via a plurality of engine accessories may be greater than is desired.
Operation of engine accessories for larger displacement engines may not result in objectionable conditions because larger displacement engines often have large amounts of engine torque reserve that may be activated in response to a change in accessory load. However, smaller engines may operate with less torque reserve so that activation of one or more engine accessories may result in a significant reduction in engine speed, or possibly an engine stall condition. If the engine is operated at higher altitudes, the engine may have even less capacity to produce torque since air density is lower at higher altitudes.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for distributing engine torque, comprising: limiting an amount of engine torque supplied to engine accessories in response to driver demand torque and available engine torque.
By limiting an amount of engine torque supplied to engine accessories based on driver demand torque and available engine torque, it may be possible to reduce the possibility of providing objectionable engine operating conditions. For example, engine accessories may be commanded to operate at torques such that when all accessory torques are added together, the torques sum to less than the limited amount of engine torque that is available to engine accessories. In this way, it may be possible to provide torque to engine accessories in an amount that reduces the possibility of engine speed variation or engine stalling.
The present description may provide several advantages. Specifically, the approach may improve distribution of engine torque to engine accessories. Further, the approach may reduce the possibility of objectionable engine operating conditions. In addition, the approach may be applied to a wide range of engine accessories. Finally, the approach may be applied to vehicles that are propelled via a motor rather than by an engine.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.